This invention relates generally to semiconductor processes, and more particularly the invention relates to a method of forming low resistance semiconductor material and resulting devices.
Modern digital electronic circuits are typically embodied in high density integrated circuits formed in and on monolithic single crystalline semiconductor bodies. The integrated circuits are defined in the monocrystalline semiconductor body by the selective introduction of dopants to define the various components of the circuit. Interconnection of the components entails the formation of metal layers or doped polycrystalline semiconductor layers from which interconnect patterns are defined through use of photoresist masking and etch techniques. The major limitations on power consumption and speed of operation of integration circuits lies in the density of the circuit and the resistivity of the interconnect lines. This limitation becomes more severe as line width is decreased to allow for higher density circuits. The disadvantages of polysilicon interconnections and gate technology due to the relative high resistivity of doped polycrystalline silicon are discussed in the Electro Chemical Society Extended Abstracts Volume 78-1 (Abstract No. 274), Volume 77-2 (Abstract No. 330, No. 331, and No. 360).
In the fabrication of semiconductor devices doping techniques are used to form the regions of P and N conductivity type. Both diffusion and ion implantation techniques are well known for introducing dopants into semiconductor material.
Diffusion typically involves a high temperature process for driving into semiconductor material dopant atoms from a vapor. Ion implantation offers greater accuracy in doping, however the lattice structure of the monocrystalline semiconductor material is damaged by ion implantation and also not all of the ions are electrically active. Therefore, annealing is required to ameliorate the lattice damage from ion implantation and activate the dopants. The annealing can be performed by heating the semiconductor body at an elevated temperature, but the high temperature causes diffusion of impurities within the semiconductor body.
Recently the use of laser irradiation has been proposed for annealing ion implantation damage in semiconductor material. The use of a laser rapidly heats selected areas of the semiconductor material without the need for heating the entire semiconductor body in a furnace.
Hutchins and Laff, IBM Technical Disclosure Bulletin Vol. 16, No. 10 March 1974, disclose the use of a scanning laser to improve polysilicon for device fabrication therein. Doping of the polysilicon is performed after the laser scanning. Fan and Zieger disclose in U.S. Pat. No. 4,059,461 the use of a laser beam to crystallize an amorphous semiconductor film formed on a substrate in a photovoltaic application.